The present invention relates to methods and compositions for treating a water- and hydrocarbon-producing subterranean formation with a relative permeability modifier, and, more specifically, to improved treatment fluids, methods for preparing treatment fluids, and methods for use thereof to reduce the water permeability of the subterranean formation without substantially reducing the hydrocarbon permeability.
The production of water from hydrocarbon-producing wells constitutes a significant technical problem and expense in oilfield operations. When a subterranean formation contains a significant amount of water, the water's higher mobility often allows it to flow to a hydrocarbon-producing zone of the formation by way of natural and manmade fractures and high permeability streaks. If the ratio of recovered water to recovered hydrocarbons becomes significantly large, the cost of separating the water from the hydrocarbons and disposing of it becomes a significant economic barrier to production.
In order to reduce the production of undesired water from hydrocarbon-producing subterranean formations, aqueous-soluble polymer solutions containing crosslinking agents have been utilized in the art to enter water-containing zones of the formation and block the flow of undesired water. Selective placement of these crosslinked polymers in a subterranean formation and stability therein represent significant technical challenges that have somewhat limited their use. A more recent strategy to reduce water production from a subterranean formation has been to utilize agents known as relative permeability modifiers. Such relative permeability modifiers are capable of reducing the flow of water through a subterranean formation while having a minimal effect on the flow of hydrocarbons. The use of relative permeability modifiers does not necessitate the use of zonal isolation techniques that are often employed with crosslinked polymers.
Although a number of relative permeability modifiers have been successfully employed in the field, some of them are unstable under certain conditions including, for example, high or low pH, excessive salinity and/or extreme temperatures that are commonly encountered downhole. For example, at temperatures greater than about 140° F., a commonly encountered relative permeability modifier precipitates at a pH of greater than about 8. Precipitation of the relative permeability modifier not only substantially terminates its relative permeability-modifying properties but also can damage a subterranean formation if the precipitation occurs downhole. Likewise, downhole precipitation can also occur in high pH fracturing fluids for similar reasons.